In the copending application of Drs. Bard and Kraeutler, Ser. No. 024,520, there are described methods for the heterogeneous photocatalytic decarboxylation of saturated carboxylic acid on several n-type semiconductor powders. Several specific semiconductor powders were disclosed as particularly advantageous for use in connection with those methods. Included were platinized TiO.sub.2 powders, such as anatase, doped and anatase, undoped.
The present invention relates to the preparation of such powders by photocatalytic deposition of metal (such as platinum in the above-noted examples) to produce powders which are especially useful as supported metal catalysts. The techniques of this invention produce catalyst materials consisting of finely dispersed metal on a semiconductor support. These materials have been found to be useful as catalysts for the purposes mentioned in the copending application referred to above, and for other processes.
The methods of this invention are also useful in depositing metal ions from a liquid having a dilute concentration of such metal ions, in situations wherein it would otherwise be difficult to rid the liquid of the metal ions. For example, industrial effluents frequently contain small quantities of copper. Since it is difficult to recover the copper, the valuable metal is lost and, perhaps more important, the metal contaminates or destroys organisms exposed to such streams.
In the past, it has been known to deposit metal on semiconductors. The photovoltaic plating of silver or copper on the inside of a silicon p-n junction has been described in the prior art, as has been the photoreduction of silver and palladium on n-type titanium dioxide. Similarly, the photoreduction of copper on n-TiO.sub.2 and n-SrTiO.sub.3 electrodes has been described in the prior art, frequently in connection with photographic studies.
Phillipp et al, U.S. Pat. No. 3,826,726, describes the deposition of metallic elements by irradiating aqueous solutions or suspensions of metal salts with high energy particles, such as electrons, protons, ions and neutrons obtained from particle accelerators and radioactive sources.
So far as applicants are aware, however, the prior art does not describe any such method suitable for the preparation of metallized powders wherein the metal is highly dispersed thereon, or for the consequent removal of metal ions from a reaction mixture.
It would be advantageous to provide such methods for the reasons mentioned above. Such methods are provided by this invention.